/*
 * Copyright (C) 2013 ARM Ltd.
 * Copyright (C) 2013 Linaro.
 *
 * This code is based on glibc cortex strings work originally authored by Linaro
 * and re-licensed under GPLv2 for the Linux kernel. The original code can
 * be found @
 *
 * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
 * files/head:/src/aarch64/
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#include <generated/kconfig.h>
#include <utils/pagesize.h>
#include <seminix/linkage.h>
#include <seminix/cache.h>
#include <asm/assembler.h>

/*
 * compare two strings
 *
 * Parameters:
 *  x0 - const string 1 pointer
 *  x1 - const string 2 pointer
 *  x2 - the maximal length to be compared
 * Returns:
 *  x0 - an integer less than, equal to, or greater than zero if s1 is found,
 *     respectively, to be less than, to match, or be greater than s2.
 */

#define REP8_01 0x0101010101010101
#define REP8_7f 0x7f7f7f7f7f7f7f7f
#define REP8_80 0x8080808080808080

/* Parameters and result.  */
src1		.req	x0
src2		.req	x1
limit		.req	x2
result		.req	x0

/* Internal variables.  */
data1		.req	x3
data1w		.req	w3
data2		.req	x4
data2w		.req	w4
has_nul		.req	x5
diff		.req	x6
syndrome	.req	x7
tmp1		.req	x8
tmp2		.req	x9
tmp3		.req	x10
zeroones	.req	x11
pos		.req	x12
limit_wd	.req	x13
mask		.req	x14
endloop		.req	x15

WEAK(strncmp)
    cbz	limit, .Lret0
    eor	tmp1, src1, src2
    mov	zeroones, #REP8_01
    tst	tmp1, #7
    b.ne	.Lmisaligned8
    ands	tmp1, src1, #7
    b.ne	.Lmutual_align
    /* Calculate the number of full and partial words -1.  */
    /*
    * when limit is mulitply of 8, if not sub 1,
    * the judgement of last dword will wrong.
    */
    sub	limit_wd, limit, #1 /* limit != 0, so no underflow.  */
    lsr	limit_wd, limit_wd, #3  /* Convert to Dwords.  */

    /*
    * NUL detection works on the principle that (X - 1) & (~X) & 0x80
    * (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
    * can be done in parallel across the entire word.
    */
.Lloop_aligned:
    ldr	data1, [src1], #8
    ldr	data2, [src2], #8
.Lstart_realigned:
    subs	limit_wd, limit_wd, #1
    sub	tmp1, data1, zeroones
    orr	tmp2, data1, #REP8_7f
    eor	diff, data1, data2  /* Non-zero if differences found.  */
    csinv	endloop, diff, xzr, pl  /* Last Dword or differences.*/
    bics	has_nul, tmp1, tmp2 /* Non-zero if NUL terminator.  */
    ccmp	endloop, #0, #0, eq
    b.eq	.Lloop_aligned

    /*Not reached the limit, must have found the end or a diff.  */
    tbz	limit_wd, #63, .Lnot_limit

    /* Limit % 8 == 0 => all bytes significant.  */
    ands	limit, limit, #7
    b.eq	.Lnot_limit

    lsl	limit, limit, #3    /* Bits -> bytes.  */
    mov	mask, #~0
CPU_BE( lsr	mask, mask, limit )
CPU_LE( lsl	mask, mask, limit )
    bic	data1, data1, mask
    bic	data2, data2, mask

    /* Make sure that the NUL byte is marked in the syndrome.  */
    orr	has_nul, has_nul, mask

.Lnot_limit:
    orr	syndrome, diff, has_nul
    b	.Lcal_cmpresult

.Lmutual_align:
    /*
    * Sources are mutually aligned, but are not currently at an
    * alignment boundary.  Round down the addresses and then mask off
    * the bytes that precede the start point.
    * We also need to adjust the limit calculations, but without
    * overflowing if the limit is near ULONG_MAX.
    */
    bic	src1, src1, #7
    bic	src2, src2, #7
    ldr	data1, [src1], #8
    neg	tmp3, tmp1, lsl #3  /* 64 - bits(bytes beyond align). */
    ldr	data2, [src2], #8
    mov	tmp2, #~0
    sub	limit_wd, limit, #1 /* limit != 0, so no underflow.  */
    /* Big-endian.  Early bytes are at MSB.  */
CPU_BE( lsl	tmp2, tmp2, tmp3 )	/* Shift (tmp1 & 63).  */
    /* Little-endian.  Early bytes are at LSB.  */
CPU_LE( lsr	tmp2, tmp2, tmp3 )	/* Shift (tmp1 & 63).  */

    and	tmp3, limit_wd, #7
    lsr	limit_wd, limit_wd, #3
    /* Adjust the limit. Only low 3 bits used, so overflow irrelevant.*/
    add	limit, limit, tmp1
    add	tmp3, tmp3, tmp1
    orr	data1, data1, tmp2
    orr	data2, data2, tmp2
    add	limit_wd, limit_wd, tmp3, lsr #3
    b	.Lstart_realigned

/*when src1 offset is not equal to src2 offset...*/
.Lmisaligned8:
    cmp	limit, #8
    b.lo	.Ltiny8proc /*limit < 8... */
    /*
    * Get the align offset length to compare per byte first.
    * After this process, one string's address will be aligned.*/
    and	tmp1, src1, #7
    neg	tmp1, tmp1
    add	tmp1, tmp1, #8
    and	tmp2, src2, #7
    neg	tmp2, tmp2
    add	tmp2, tmp2, #8
    subs	tmp3, tmp1, tmp2
    csel	pos, tmp1, tmp2, hi /*Choose the maximum. */
    /*
    * Here, limit is not less than 8, so directly run .Ltinycmp
    * without checking the limit.*/
    sub	limit, limit, pos
.Ltinycmp:
    ldrb	data1w, [src1], #1
    ldrb	data2w, [src2], #1
    subs	pos, pos, #1
    ccmp	data1w, #1, #0, ne  /* NZCV = 0b0000.  */
    ccmp	data1w, data2w, #0, cs  /* NZCV = 0b0000.  */
    b.eq	.Ltinycmp
    cbnz	pos, 1f /*find the null or unequal...*/
    cmp	data1w, #1
    ccmp	data1w, data2w, #0, cs
    b.eq	.Lstart_align /*the last bytes are equal....*/
1:
    sub	result, data1, data2
    ret

.Lstart_align:
    lsr	limit_wd, limit, #3
    cbz	limit_wd, .Lremain8
    /*process more leading bytes to make str1 aligned...*/
    ands	xzr, src1, #7
    b.eq	.Lrecal_offset
    add	src1, src1, tmp3	/*tmp3 is positive in this branch.*/
    add	src2, src2, tmp3
    ldr	data1, [src1], #8
    ldr	data2, [src2], #8

    sub	limit, limit, tmp3
    lsr	limit_wd, limit, #3
    subs	limit_wd, limit_wd, #1

    sub	tmp1, data1, zeroones
    orr	tmp2, data1, #REP8_7f
    eor	diff, data1, data2  /* Non-zero if differences found.  */
    csinv	endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
    bics	has_nul, tmp1, tmp2
    ccmp	endloop, #0, #0, eq /*has_null is ZERO: no null byte*/
    b.ne	.Lunequal_proc
    /*How far is the current str2 from the alignment boundary...*/
    and	tmp3, tmp3, #7
.Lrecal_offset:
    neg	pos, tmp3
.Lloopcmp_proc:
    /*
    * Divide the eight bytes into two parts. First,backwards the src2
    * to an alignment boundary,load eight bytes from the SRC2 alignment
    * boundary,then compare with the relative bytes from SRC1.
    * If all 8 bytes are equal,then start the second part's comparison.
    * Otherwise finish the comparison.
    * This special handle can garantee all the accesses are in the
    * thread/task space in avoid to overrange access.
    */
    ldr	data1, [src1,pos]
    ldr	data2, [src2,pos]
    sub	tmp1, data1, zeroones
    orr	tmp2, data1, #REP8_7f
    bics	has_nul, tmp1, tmp2 /* Non-zero if NUL terminator.  */
    eor	diff, data1, data2  /* Non-zero if differences found.  */
    csinv	endloop, diff, xzr, eq
    cbnz	endloop, .Lunequal_proc

    /*The second part process*/
    ldr	data1, [src1], #8
    ldr	data2, [src2], #8
    subs	limit_wd, limit_wd, #1
    sub	tmp1, data1, zeroones
    orr	tmp2, data1, #REP8_7f
    eor	diff, data1, data2  /* Non-zero if differences found.  */
    csinv	endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
    bics	has_nul, tmp1, tmp2
    ccmp	endloop, #0, #0, eq /*has_null is ZERO: no null byte*/
    b.eq	.Lloopcmp_proc

.Lunequal_proc:
    orr	syndrome, diff, has_nul
    cbz	syndrome, .Lremain8
.Lcal_cmpresult:
    /*
    * reversed the byte-order as big-endian,then CLZ can find the most
    * significant zero bits.
    */
CPU_LE( rev	syndrome, syndrome )
CPU_LE( rev	data1, data1 )
CPU_LE( rev	data2, data2 )
    /*
    * For big-endian we cannot use the trick with the syndrome value
    * as carry-propagation can corrupt the upper bits if the trailing
    * bytes in the string contain 0x01.
    * However, if there is no NUL byte in the dword, we can generate
    * the result directly.  We can't just subtract the bytes as the
    * MSB might be significant.
    */
CPU_BE( cbnz	has_nul, 1f )
CPU_BE( cmp	data1, data2 )
CPU_BE( cset	result, ne )
CPU_BE( cneg	result, result, lo )
CPU_BE( ret )
CPU_BE( 1: )
    /* Re-compute the NUL-byte detection, using a byte-reversed value.*/
CPU_BE( rev	tmp3, data1 )
CPU_BE( sub	tmp1, tmp3, zeroones )
CPU_BE( orr	tmp2, tmp3, #REP8_7f )
CPU_BE( bic	has_nul, tmp1, tmp2 )
CPU_BE( rev	has_nul, has_nul )
CPU_BE( orr	syndrome, diff, has_nul )
    /*
    * The MS-non-zero bit of the syndrome marks either the first bit
    * that is different, or the top bit of the first zero byte.
    * Shifting left now will bring the critical information into the
    * top bits.
    */
    clz	pos, syndrome
    lsl	data1, data1, pos
    lsl	data2, data2, pos
    /*
    * But we need to zero-extend (char is unsigned) the value and then
    * perform a signed 32-bit subtraction.
    */
    lsr	data1, data1, #56
    sub	result, data1, data2, lsr #56
    ret

.Lremain8:
    /* Limit % 8 == 0 => all bytes significant.  */
    ands	limit, limit, #7
    b.eq	.Lret0
.Ltiny8proc:
    ldrb	data1w, [src1], #1
    ldrb	data2w, [src2], #1
    subs	limit, limit, #1

    ccmp	data1w, #1, #0, ne  /* NZCV = 0b0000.  */
    ccmp	data1w, data2w, #0, cs  /* NZCV = 0b0000.  */
    b.eq	.Ltiny8proc
    sub	result, data1, data2
    ret

.Lret0:
    mov	result, #0
    ret
ENDPIPROC(strncmp)
